Passenger Audra D. Bridges posted the video on Facebook after the incident Sunday evening. It shows the guards grabbing the screaming man from a window seat and pulling him across the armrest before dragging him down the airplane aisle by his arms.

Other passengers are heard saying, "Please, my God. What are you doing? No. This is wrong. Oh my God. Look at what you did to him" and "Busted his lip."

Bridges, of Louisville, told The (Louisville) Courier-Journal (http://cjky.it/2oQtLIA ) that after the passengers had boarded the flight to Louisville, Kentucky, they were told that four volunteers were needed to give up their seats for stand-by United employees who needed to be in Louisville on Monday for a flight. She said they were told the flight wouldn't depart until the employees were seated.

United spokesman Charlie Hobart said airline employees named four customers who had to leave the plane and that three of them did so. He said law enforcement was called when the fourth person refused to get off the plane.

"We followed the right procedures," Hobart told the Associated Press in a phone interview. "That plane had to depart. We wanted to get our customers to their destinations, and when one gentleman refused to get off the aircraft, we had to call the Chicago Police Department."

Bridges said passengers were told a computer selected four people to leave the flight. One couple was selected and left the plane before the man was confronted.

"Everyone was shocked and appalled," Bridges said. "There were several children on the flight as well that were very upset."

Hobart said he didn't know how the airline compensated the passengers who were forced to deplane. Bridges said the airline offered $800 and a hotel stay.